Ferrous seal sliding parts and producing method thereof

ABSTRACT

A ferrous seal sliding part excellent in heat crack resistance, seizing resistance and abrasion resistance is provided. The ferrous seal sliding part having a seal sliding surface, wherein the seal sliding surface has a martensite parent phase which forms a solid solution with carbon of 0.15 to 0.6 wt % and contains a first dispersion material of at least either cementite of 5 to 70% by volume or MC-type carbide of 0.1 to 10% by volume and a second dispersion material of at least either graphite of 1 to 15% by volume or Cu alloy phase of 1 to 20% by volume dispersed therein, with a total content of the first dispersion material and the second dispersion material being 5 to 70% by volume.

FIELD OF THE INVENTION

The present invention relates to ferrous seal sliding parts availablefor floating seal members such as rollers, idlers and reduction gearsfor construction machines and a producing method thereof.

BACKGROUND OF THE INVENTION

A track roller assembly and a reduction gear apparatus of a constructionmachine are equipped with ferrous floating seal parts for the purpose ofpreventing leakage of lubrication oil from inside thereof as well asentering of earth and sand therein. Accordingly, such floating sealparts are widely produced by applying adequate treatment in which a sealsliding surface thereof is quenched to have a hard martensite structure,or a large amount of hard cementite and Cr₇C₃ carbide of 30% by volumeare crystallized in the seal sliding surface while causing a parent,phase to a martensite by quenching, in order to improve seizingresistance and abrasion resistance. Such an exemplary floating seal partis made by using a Ni-hard cast iron (having a typical composition ofcarbon of 2.7 to 3.5 wt %, Si of 0.4 to 1.0 wt %, Mn of 0.4 to 0.6 wt %,Ni of 4.2 to 4.7 wt % and Cr of 1.4 to 2.5 wt %), a high-carbon andhigh-Cr cast iron (for example, carbon of 3.3 to 3.6 wt %, Cr of 15 to17 wt %, Mo of 2.5 to 3.5 wt % and V of 0.2 to 0.5 wt %) (for example,as shown in Japanese Patent Publication (KOKAI) No. S51-59007).

In addition, a ferrous floating seal part in which claddingabrasion-resistant material containing of WC and self-fluxing alloy issplayed to a seal sliding surface thereof is sometime used for somepurposes.

In the ferrous floating seal part used for sealing a lubricating oil inthe reduction gears and the track rollers, a seal sliding surfacethereof is abraded as fine particles of earth and sand are entered onthe seal sliding surface by hulling motion in the earth and sand, and islubed with the sealed lubrication oil therein. Accordingly, a ferrousfloating seal part capable of withstanding a very severe lubricationcondition is required. Even in a case of a most conventionally used hardferrous floating seal part made of a high-carbon and high-Cr cast iron,when setting pressure (press force) at assembling is high, considerablequenching crack (heat crack), seizing and abnormal abrasion occur on theseal sliding surface, resulting in leakage of oil.

And, even if various tool steels such as a cold work tool steel and ahigh speed steel (SKH material) are applied so as to increase theseizing resistance and the abrasion resistance, seizing due to defect ofseizing resistance easily occurs, resulting in insufficient heat crackresistance and abrasion resistance. In addition, since such steels areso expensive that a material costs would increase in view of materialyields before a product is finished.

Further more, in resent years, construction machines such as bulldozerare required to be driven at a high speed for improvement in workingefficiency, and therefore, the ferrous floating seal part necessarilyrotates at a high speed. This also causes quenching crack, seizing andabnormal abrasion, resulting in leakage of oil.

In order to solve the above-mentioned problem, an object of the presentinvention is to provide ferrous seal sliding parts excellent in heatcrack resistance, seizing resistance and abrasion resistance and aproducing method thereof.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a ferrousseal sliding part having a seal sliding surface, wherein the sealsliding surface has a martensite parent phase which forms a solidsolution with carbon of 0.15 to 0.6 wt % and contains a first dispersionmaterial of at least either cementite of 5 to 70% by volume or MC-typecarbide of 0.1 to 10% by volume and a second dispersion material of atleast either graphite of 1 to 15% by volume or Cu alloy phase of 1 to20% by volume dispersed therein, with a total content of the firstdispersion material and the second dispersion material being 5 to 70% byvolume.

A ferrous seal sliding part according to the present invention has aseal sliding surface, wherein the seal sliding surface is formed byusing a cast iron containing carbon of 2 to 5 wt %, Si of 0.5 to 6 wt %,Cr of 0.3 to 5 wt % and one or more alloy element selected from thegroup consisting of Al, Mn, Ni, Cu, Co, Mo, W, V, Ti, Zr, Nb, Ta, P, B,Ca and S.

In the present invention, it is also possible that the ferrous sealsliding part is made by casting using the aforesaid cast iron.

And, it is also possible that the ferrous seal sliding part is afloating seal part made by casting using the aforesaid cast iron.

A producing method of a ferrous seal sliding part according to thepresent invention comprises a step for casting a cast iron containingcarbon of 2 to 5 wt %, Si of 0.5 to 6 wt %, Cr of 0.3 to 5 wt % and oneor more alloy element selected from the group consisting of Al, Mn, Ni,Cu, Co, Mo, W, V, Ti, Zr, Nb, Ta, P, B, Ca and S, wherein the sealsliding part has a martensite parent phase which forms a solid solutionwith carbon of 0.15 to 0.6 wt % and contains a first dispersion materialof at least either cementite of 5 to 70% by volume or MC-type carbide of0.1 to 10% by volume and a second dispersion material of at least eithergraphite of 1 to 15% by volume or Cu alloy phase of 1 to 20% by volumedispersed therein, with a total content of the first dispersion materialand the second dispersion material being 5 to 70% by volume.

EFFECT OF THE INVENTION

As described above, the present invention will provide ferrous sealsliding parts excellent in heat crack resistance, seizing resistance andabrasion resistance and a producing method thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing showing a thermodynamically calculated phase diagramof a mixture of ferrite and austenite and an austenite phase of amaterial containing iron, Si of 4.5 wt %, carbon and M (alloy element).

FIG. 2 is a drawing showing a main part of a roller assembly accordingto one embodiment of the present invention.

FIG. 3 are drawings showing various structures of graphite crystallizedand dispersed in a cast iron formed by casting.

FIG. 4A is a photograph showing a casting structure of Ni-hardcomparative material and FIG. 4B is a photograph showing a heat treatedstructure thereof after graphitizing.

FIG. 5 is a cross sectional drawing showing a floating seal.

FIG. 6 is a drawing schematically showing a floating seal tester.

DETAILED DESCRIPTION OF EMBODIMENT OF THE INVENTION

The present invention is to provide a cast iron sliding material havingthe following properties, which is used for a floating seal part.

(1) Hard cementite, having small scraping characteristics against thecounterpart surface to a sliding surface and high toughness, isdispersed in a martensite parent phase in 5 to 70% by volume so as toimprove adhesion resistance and abrasion resistance.

(2) At least either graphite or Cu alloy phase, excellent in adhesionresistance and capability for supplying an lubricating oil to a sealsliding surface (oil pocket forming capability), is dispersed andprecipitated in 1 to 20% by volume so as to improve lubricating propertyof the seal sliding surface, therefore to improve seizing resistance.

(3) In order to improve heat crack resistance of a martensite parentphase, a concentration of carbon in the martensite parent phase isadjusted as small as to 0.15 to 0.6 wt %.

(4) In order to increase tempering-softening resistance of martensiteand to adjust an amount of retained austenite improving conformability,an alloy element such as Si, Al, Ni, V, Mo and W should be suitablyadded.

(5) MC-type carbide of V, Ti, Zr, Nb, Ta and the like is dispersed so asto improve adhesion resistance and abrasion resistance.

A floating seal part, which is an exemplary ferrous seal sliding partaccording to the present invention, requires higher heat crackresistance, seizing resistance and abrasion resistance withstanding asevere use condition. A floating seal part according to the presentinvention is made by a ferrous seal sliding material having a martensitephase which forms a solid solution with carbon of 0.15 to 0.6 wt % toimprove heat crack resistance and contains at least either cementite of5 to 70% by volume or MC-type carbide of 0.1 to 10% by volume dispersedtherein to improve seizing resistance and abrasion resistance and atleast either graphite of 1 to 15% by volume or Cu alloy phase of 1 to20% by volume dispersed therein to improve seizing resistance, with atotal content of at least either the cementite or the MC-type carbideand at least either the graphite or the Cu alloy phase being 5 to 70% byvolume.

The ferrous seal sliding material employs a cast iron containing carbonof at least 2 to 5 wt %, Si of 0.5 to 6 wt %, Cr of 0.3 to 5 wt % andone or more alloy element selected from the group consisting of Al, Mn,Ni, Cu, Co, Mo, W, V, Ti, Zr, Nb, Ta, P, B, Ca and S.

In the present invention, in order to improve heat crack resistance, asliding surface of a floating seal part is made to have a martensiteparent phase containing carbon of 0.15 to 0.6 wt %. Because, it issupposed that a ferrous floating seal part made of the aforesaidhigh-carbon and high-Cr cast iron has a martensite phase containingcarbon of about 0.8 wt %, and therefore, the upper limit of an amount ofcarbon which forms a solid solution with a martensite phase ispreferably set at 0.7 wt %. However, in view of a concentration ofcarbon contained in a hot work tool steel (SKD6, SKD7, SKD61, SKD62,SKD8 and 3Ni-3Mo steel) which requires high heat crack resistance, it ispreferred that the upper limit of an amount of carbon which forms asolid solution with a martensite phase is set at 0.6 wt % and the lowerlimit thereof is set at 0.15 wt %.

In addition, in order to further improve abrasion resistance to enteringof earth and sand, it is preferable that the martensite parent phase hashardness of Hv500 or more. And, in order to ensure more stable heatcrack resistance, it is more preferable that a concentration of carbonwhich forms a solid solution with the martensite parent phase isadjusted to within the range of 0.15 to 0.5 wt %.

Next, a method for adjusting a concentration of carbon, which forms asolid solution with a quench hardened martensite parent phase to theaforesaid range, will be explained. In order to cause a matrix of a castiron to have a stable pearlite structure, it is preferable that Cr of0.3 wt % or more is contained.

(Method 1) When a cast iron to be a pearlite structure is quenchedduring casting, a concentration of Si in an austenite phase (amartensite phase after quenching) is adjusted to 2 wt % or more, andpreferably 3 wt % or more, by using the following method. That is, aeutectoid carbon concentration of a pearlite structure containing ironand carbon is about 0.8 wt %, and the concentration may decrease byaddition of Si, remarkably increasing carbon activity in an austenitephase, at a ratio of an amount of carbon of 0.1 wt % per an amount of Siof 1 wt %.

Si hardly forms a solid solution with graphite, cementite and MC-typecarbide but almost all Si is concentrated in a martensite phase.Accordingly, for example, in a cast iron in which cementite is dispersedin 40% by volume, in order to obtain a martensite phase containing Si of3 wt %, Si of 1.8 wt % may be added to the cast iron. And, when a totalcontent of cementite and graphite is a preferable lower limit of 16% byvolume, as described later, in order to adjust a concentration of carbonwhich forms a solid solution with a martensite parent phase to withinthe range of 0.15 to 0.6 wt %, Si of 1.5 to 6 wt % may be added to thecast iron. And, since Cr has substantially the same capability todecrease a eutectoid carbon concentration as Si, it is preferable that atotal amount of Si and Cr in a martensite parent phase is adjusted to 2wt % or more, and preferably 3 to 6.5 wt %. Therefore, in the presentinvention, it is preferable that a cast iron contains Si of at least 1.8to 6 wt % so that a concentration of Si in a martensite parent phasewill be adjusted to 3 to 6.5 wt %. The upper limit of an amount of Siadded to the cast iron is set at 6 wt % for the purpose of toughness.

Another method for adjusting a concentration of carbon which forms asolid solution with a martensite parent phase to the aforesaid rangewill be explained.

(Method 2) In a case of a cast iron in which graphite and ferrite phaseare precipitated, it is preferable that the cast iron is heated to Altransformation temperature or more, whereby carbon in the graphite isdiffused in and forms a solid solution with austenite, and then directlyquenched after a heat treatment for causing the ferrite phase to bedisappeared.

(Method 3) After the heating treatment of the method 2, the cast iron iscooled down to cause a parent phase to have a pearlite structure or astructure in which granulated cementite is dispersed, and then quenched.

At this time, the quenching treatment is preferably carried out suchthat the cast iron is induction heated at only a sliding surface thereofat a heating rate of 150° C./sec or more to cause pearlitely platycementite or granulated cementite to remain in a martensite parent phasewithout forming a solid solution therewith. In such a case, aconcentration of carbon which forms a solid solution with the martensitephase can be adjusted depending on a concentration of Cr in cementite.Accordingly, adjusting a concentration of Cr in cementite to 4 to 15 wt% will allow a concentration of carbon which forms a solid solution withthe martensite phase to 0.15 to 0.6 wt %. And, the concentration of thecarbon decreases depending on a concentration of Si in austenite at arate of an amount of carbon of 0.1 wt % per an amount of Si of 1 wt %.For example, when Si of 4 wt % is contained, Cr of 2.5 wt % may becontained in cementite. So, a range of concentration of Cr in cementiteis preferably 2.5 to 15 wt %. Accordingly, in the present invention, itis preferable that a cast iron contains at least Si of 0.5 to 1.5 wt %and Cr of 0.9 to 5 wt % so that a total amount of Si and Cr in amartensite parent phase will be adjusted to 2 to 4 wt % and an amount ofCr in cementite will be adjusted to 2.5 to 15 wt %.

In addition, a structure, in which cementite in addition to cementitecrystallized in a martensite phase by a eutectic reaction, are finelyand pearlitely dispersed in a martensite parent phase, enhancescapability for supplying a lubricating oil to a sliding surface of afloating seal part and also enhances abrasion resistance of a parentphase. Accordingly, such the structure is preferable for a ferrous sealsliding material according to the present invention.

When a martensite phase contains Si of 4 wt % or more, as calculatedfrom a HANSEN'S phase diagram of iron and Si, a Fe₃Si order-disordertransformation is demonstrated so that tempering-softening resistanceand adhesion resistance of a sliding surface will be significantlyimproved. However, when a martensite phase contains Si of 7 wt % ormore, ordered phases appear, causing remarkable brittleness.Accordingly, it is preferred that a concentration of Si in a martensiteparent phase is adjusted to 4 to 6.5 wt %, and it is more preferred thata concentration of carbon which forms a solid solution with themartensite parent phase is adjusted within the range of 0.15 to 0.4 wt%.

As described later, an alloy element demonstrating the order-disordertransformation includes Al which has little solid solubility withcementite, as well as Si. Therefore, in the present invention, anaddition of Al is preferred. However, Al has a little capability todecrease a concentration of carbon which forms a solid solution with amartensite phase. Accordingly, it is preferable that a solid solubleconcentration of carbon with a martensite parent phase is adjusted byadjusting an amount of Si contained in the martensite parent phase andthe order-disorder transformation is demonstrated by adding of Al withSi. This prevents brittleness and improves seizing resistance andabrasion resistance.

In the present invention, it is preferable that the cast iron containsAl of 0.5 to 6 wt % so that a concentration of Al in a martensite parentphase will be adjusted to 1 to 12 wt %.

Si in a martensite phase is a typical element to increasetempering-softening resistance, and especially increasestempering-softening resistance higher than Mo and W in a low temperatureregion under 450° C.; however, smaller than Mo and W in a hightemperature region over 450° C. Accordingly, it is preferable to make analloy element, such as Mo and W, positively form a solid solution. In acase of addition of Mo and W coexistent with Si, when Mo of less than ahighest effective addition amount of 2.3-0.5×an amount of Si (wt %) isadded, softening-tempering resistance of Mo can be efficientlydemonstrated. And, a distribution coefficient γKMo of Mo betweencementite and austenite, which are crystallized during solidification,is shown by dividing a concentration (wt %) of Mo in the cementite by aconcentration (wt %) of Mo in the austenite. The γKMo of Mo is 2 to 2.5,and a maximum solid solubility limit of Mo with cementite is about 2 wt%, at which a concentration Mo in a martensite parent phase is about 1wt %. Therefore, in a ferrous seal sliding material according to thepresent invention, it is preferable that a cast iron contains Si of 1 to3 wt % and Mo and W in a total amount of 0.5 to 2 wt % so that in amartensite parent phase an amount of Si will be adjusted to 2 to 4 wt %and a total amount of Mo and W will be adjusted to 0.5 to 1 wt %. And,in order to enhance tempering-softening resistance in a low temperatureregion and further enhance it in a high temperature region, it ispreferable that Mo of 0.5 to 2 wt % is added to the cast iron so that anamount of Mo in a martensite parent phase can be adjusted to 0.3 to 1 wt%. And, since W has a distribution coefficient γKW of about 1.5 and amaximum solid solubility limit with cementite is 2 wt %, as the resultof the same study as Mo, W works efficiently more than or equal to Mo.Accordingly, in the present invention, it is preferred that Mo and W ina total amount of 0.5 to 2 wt % is added to the cast iron. The upperlimit of a total addition amount of Mo and W is determined such thatFe₃MO₃C₆-type special carbide is precipitated in a small amount and Moand W of a largest amount capable of coexisting with cementite form asolid solution with a martensite parent phase. An addition of Mo and Win an amount larger than the upper limit is not preferable from aneconomical viewpoint. Since Mo special carbide (Fe₃MO₃C) is used as amaterial for a conventional high-carbon and high-CrMo floating sealpart, seizing resistance and abrasion resistance will not decline.

An element to increase a carbon activity in an austenite phase so as todecrease a solid soluble concentration of carbon with austenite includesP, in addition to Si. P, however, has a solid solubility limit withaustenite of under 1 wt %, whereby capability to decrease a solidsoluble concentration of carbon is small. But, since precipitated Fe₃Pphosphide improves seizing resistance of a sliding surface, it ispreferred that P of 1.5 wt % or less, at which the cast iron is notembrittled so much, is added.

The present invention proposes dispersion of MC-type carbide of 0.1 to10% by volume, as described above. So, a dispersion of very hard MC-typecarbide, excellent in adhesion resistance, of 0.1% or more by volumesignificantly improves adhesion resistance as well as seizing resistanceof a sliding surface (refer to hard particles dispersion effect). On theother hand, since a high speed steel in which V₄C₃ is dispersed in about10% by volume improves abrasion resistance to earth and sand, it ispreferable that an upper limit of addition amount of MC-type carbide is10% by volume from an economical viewpoint for precipitating MC-typecarbide. Accordingly, a cast iron abrasion resistant sliding material inwhich MC-type carbide and at least either graphite or Cu alloy phase,which improve lubricating property of a sliding surface, are dispersedin a martensite parent phase is suitable for a floating seal part. Inorder to more increase abrasion resistance to earth and sand, it ispreferable that a content of MC-type carbide is adjusted to 2 to 10% byvolume.

In a cast iron used for a floating seal part which requires abrasionresistance to entering of earth and sand, it is preferable that alargest amount of hard carbide is dispersed. Accordingly, the presentinvention proposes dispersion of inexpensive cementite of 5 to 70% byvolume. The reason that the lower limit of a content of cementite is setat 5% by volume is, for example, that a high speed steel extremelyexcellent in abrasion resistance has carbide, of which a content isadjusted to 5 to 17% by volume after quenching. Furthermore, in order toimprove seizing resistance and abrasion resistance capable ofwithstanding a severe oil sliding condition, demonstrating a lot morehard particles dispersion effect will be effective. Especially, whenabrasion resistance is important factor, it is preferable that the lowerlimit thereof is 15% by volume in view of the aforesaid high speedsteel. Accordingly, mixing the cementite with the MC-type carbideimproves the seizing resistance and the abrasion resistance moreeffective. Furthermore, dispersing at least either graphite or Cu alloyphase improves seizing resistance and adhesion resistance. In addition,it is preferable that Cu alloy phase is dispersed in the martensiteparent phase in 1 to 10% by volume.

In order to enhance abrasion resistance to entering of earth and sandand seizing resistance, it is effective to disperse cementite in alarger amount. Accordingly, in the present invention, the upper limit ofa content of cementite is set at 70% by volume, and, more preferably 50%by volume, because a ferrous floating seal part made of the high-carbonand high-Cr cast iron containing carbide dispersed therein in 50% ormore by volume becomes brittles excessively.

Accordingly, it is preferable that an amount of carbon added to the castiron should be 2 to 5 wt % in view of the lower and upper limits of thecementite. When the addition amount of carbon exceeds 4 wt %, verycoarse primary cementite will be crystallized in a large amount,resulting in becoming brittles. Accordingly, it is preferable that theadded carbon is partially precipitated as graphite and dispersed. Thus,it is preferable that granulated graphite having an average grain sizeof 15 μm or less, is dispersed in a martensite parent phase in 1 to 10%by volume.

In a cast iron abrasion resistant sliding material according to thepresent invention, Si is added in a high density. Since Si is agraphitization element, when the material is solidificated at aconventional cooling rate, the material is changed in the structuredepending on an addition amount of Si according to a relation ofMaurer's cast iron structure diagram. For example, when an additionamount of Si is smaller than 0.6×(4.3−an addition amount of carbon (wt%)), the structure is changed to have a structure of a white cast iron.When an addition amount of Si is larger than 0.6×(4.3−an addition amountof carbon (wt %)), the structure is changed to have a structure in whichgraphite is dispersed in a pearlite parent phase. And, when an additionamount of Si is equal to or larger than 1.65×(4.3−an addition amount ofcarbon (wt %)), the structure is changed to have a structure in whichgraphite is dispersed in a ferrite parent phase. It becomes difficult todisperse eutectic cementite in a cast iron according to the presentinvention, to which a larger amount of Si is added, as described above.Accordingly, in order to stabilize the eutectic cementite, it ispreferable that Cr of 0.9 wt % or more is added so that the cementitewill be likely to be graphitized by graphitization. At this time, it ispreferable that Cr within the range of 0.9 to 3.5 wt % is added so thatan amount of Cr in the cementite will be within the range of 2.5 to 6 wt%. On the other hand, a distribution coefficient γKCr of Cr betweencementite and austenite, which are crystallized during solidification,is shown by dividing a concentration (wt %) of Cr in the cementite by aconcentration (wt %) of Cr in the austenite. Cr has a distributioncoefficient γKCr of about 4. Thus, when cementite of the lower limit of15% by volume is dispersed, the lower limit of an amount of Cr added tothe cast iron is calculated as 0.9 wt %. When a concentration of Cr incementite exceeds 10 wt %, graphitization will not precede, even ifprocessing time is lengthened. Accordingly, as described later, in theabrasion resistant sliding material in which a suitable amount ofgraphite is dispersed by graphitization in a short period, it ispreferable from an economical viewpoint that the upper limit of anaddition amount of Cr is set at 3.5 wt % so that a concentration of Crin cementite will be 6 wt %.

Mn is an element which stabilizes cementite so as to suppressgraphitization of the cementite, and it is not prevented that Mn of anamount of 0.1 wt % or more is included in a cast iron. And, an additionof Mn of 5 wt % or more changes the cast iron to a white cast iron. Fromthe result, it is found that a distribution coefficient γKMn of Mn is1.5 to 2, and that containing Mn of 10 wt % or more allows stabilizationof the eutectic cementite. Consequently, although Mn is not expected tohave so much capability to stabilize eutectic cementite as Cr, it isstill preferable that Mn is positively added. And, as described later,Mn is an element to stabilize austenite significantly as well as Ni, andenhances hardenability so as to form a retained austenite phase. Inaddition, Mn is inexpensive. Thus, it is preferable that Mn of 0.7 to 5wt % is positively added. For example, when Mn of 5 wt % is added to acast iron in which cementite is dispersed in 50% by volume, aconcentration of Mn in a martensite parent phase becomes about 3.3 wt %,and as a result, austenite is stabilized so that ferrite formationduring solidification will be suppressed, and good hardenability, inaddition to a suitable amount of retained austenite formation, will beachieved.

A content F (% by volume) of retained austenite in a martensite parentphase is experientially calculated by using Ms temperature (martensitetransformation temperature) of the martensite parent phase and afollowing equation (d).F=100 exp(−0.011×(Ms−Q))  (d)

In turn, the Ms temperature is calculated by using a composition of themartensite parent phase and a following approximate equation (e).Ms(K)=993-514×an amount of carbon(wt %)^(1/2)−20×an amount of Si(wt%)+23×an amount of Al(wt %)−46×an amount of Mn(wt %)−30×an amount ofCr(wt %)−21×an amount of Ni(wt %)−9×an amount of Cu(wt %)−20×an amountof Mo(wt %)  (e)

Here, Q means a cooling temperature of 303K (Kelvin).

Using those equations makes it easier to adjust an amount of retainedaustenite.

In the approximate equation (e), an amount of carbon (wt %) means acontent of carbon in the martensite parent phase; an amount of Si (wt %)means a content of Si in the martensite parent phase; an amount of Al(wt %) means a content of Al in the martensite parent phase; an amountof Mn (wt %) means a content of Mn in the martensite parent phase; anamount of Cr (wt %) means content of Cr in the martensite parent phase;an amount of Ni (wt %) means a content of Ni in the martensite parentphase; an amount of Cu (wt %) means a content of Cu in the martensiteparent phase; and an amount of Mo (wt %) means a content of Mo in themartensite parent phase.

In the present invention, it is preferable that the cast iron containsMn of 0.7 to 5 wt % so that a concentration of Mn in a martensite parentphase will be 2 to 4 wt %, Ms temperature obtained by the approximateequation (e) will be adjusted to 95 to 260° C., and retained austenitewill remain in the martensite parent phase in 10 to 50% by volume.

Ni and Cu each having distribution coefficient γKNi of 0.3 and γKCu of 0are elements to promote graphitization of cementite. And, they areconcentrated in a martensite parent phase more effectively than Mn so asto stabilize austenite remarkably. As a result, hardenability isenhanced and retained austenite is formed. Accordingly, it is preferablethat Ni and Cu are positively added. And, Cu of 2 wt % contained in amatrix parent phase has capability to stabilize austenite (describedbelow) and to lower the Ms temperature, correspondent to that of Ni of 1wt %.

It is apparently effective for improvement in abrasion resistance thatharder particles, such as special carbide, nitride and carbonitride, aredispersed. If a larger amount of Cr and Mn is added, Cr and Mn of 36 wt% or more can form a solid solution with cementite. However, if a largeramount of Mo, W, V and Ti are added, Mo of 2 wt %, W of 1.5 wt %, V of0.6 wt % and Ti of about 0 wt % forms a solid solution with cementite.Since almost all of such alloy elements are precipitated as specialcarbide and nitride thereof, they hardly work on stabilization ofcementite, and therefore cannot prevent graphitization. Accordingly, itis possible that special carbide of Mo, W, V and Ti improving seizingresistance and abrasion resistance are effectively dispersed in the castiron in which graphite is dispersed. And, it is preferable that an alloyelement such as V, Ti, Nb, Zr, Ta and Hf, having good seizing resistanceand capable of forming very hard MC-type carbide, of 1 wt % or more,similar to the high speed steel, is added so as to disperse MC-typecarbide of 2 to 10 wt %, thereby to improve seizing resistance andabrasion resistance.

In other words, in the present invention, it is preferable that the castiron contains one or more alloy element selected from the groupconsisting of V, Ti, Zr, Nb and Ta in a total amount of 1 to 5 wt % sothat at least any one of MC-type carbide, nitride and carbonitride ofthe aforesaid alloy element will be dispersed in a martensite parentphase in 2 to 10% by volume.

When the method (2) and the method (3) for adjusting a solid solubleconcentration of carbon with a martensite parent phase are applied, in acase of a cast iron in which at least any one of graphite flake, nodulargraphite and vermicular graphite is dispersed in a parent phase ofeither ferrite or a mixture of ferrite and pearlite at casting process,it is required that the cast iron is heated to Al transformationtemperature or more, thereby to form a solid solution of a part of thegraphite so as to have a solid soluble concentration of carbon to theaforesaid concentration, and then quenched. In this case, it ispreferable that after heating to Al temperature or more, once cooleddown so as to transform a parent phase to a pearlite structure, and thenquenched. In a case of a cast iron in which large eutectic cementite isdispersed in martensite, bainite and pearlite in the casting process, itis preferable that the quenching is carried out after a heat treatmentfor graphitization, or a heat treatment for concentrating Cr and thelike in cementite. The quenching is preferably carried out such that asliding surface is quenched by the aforesaid rapid induction heating,and more preferably quenched after heating within the temperature rangeof Al transformation temperature to a quenching temperature (900 to1100° C.) at a heating rate of 150° C./sec or more, preferably 500°C./sec or more. This causes fine cementite, in addition to largecrystallized cementite, to disperse in a martensite parent phase withoutforming a solid solution therewith. A structure in which cementite ispearlitely dispersed in martensite is suitable structure for a cast ironabrasion resistant sliding material because of improvement inlubricating property of lubrication oil of a sliding surface.

The present invention is to provide a ferrous seal sliding part, whereina cast iron containing carbon of 2 to 5 wt %, Si of 0.5 to 6 wt %, Cr of0.3 to 5 wt % and one or more alloy element selected from the groupconsisting of Al, Mn, Ni, Cu, Co, Mo, W, V, Ti, Zr, Nb, Ta, P, B, Ca andS is used so that a martensite parent phase will form a solid solutionwith carbon of 0.15 to 0.6 wt % and contain a first dispersion materialof at least either cementite of 5 to 70% by volume or MC-type carbide of0.1 to 10% by volume and a second dispersion material of at least eithergraphite of 1 to 15% by volume or Cu alloy phase of 1 to 20% by volumedispersed therein, with a total content of the first dispersion materialand the second dispersion material being 5 to 70% by volume.

The aforesaid graphite includes at least any one of graphite flake,nodular graphite and vermicular graphite, which are formed atsolidification process of the cast iron. However, in order to finely andevenly disperse very soft graphite which would work as a solidlubricant, as well as in order to disperse a larger amount of cementite,in the present invention, it is preferable that the graphite istransformed to a white cast iron and then graphitization tempered toform granulated graphite having an average grain size of 15 μm or less.And, regulating a condition of the graphitization tempering conditionwill cause a large amount (15 to 50% by volume) of cementite to remainwhile the large eutectic cementite being homogenized and dispersed,thereby to improve in seizing resistance and abrasion resistance.

And, it is preferable that a dispersion content of cementite is 15 to50% by volume, as described above. On the other hand, a dispersioncontent of graphite is preferably determined such that the lower limitthereof is 1% by volume at which lubrication property as a solidlubricant and an oil pocket inherent in graphite is obviouslydemonstrated and the upper limit is 15% by volume, which is a maximumcontent of graphite in a conventional cast iron, and more preferably 10%by volume, at which the lubricating property is saturated and toughnessis obtained. In addition, although the lower limit is determined basedon the fact that a sliding material with dispersion of graphite of 1% byvolume improves seizing resistance remarkably, it is more preferablethat the lower limit of graphite to be dispersed is of 3% or more byvolume.

Cu alloy particles are often utilized as a sliding material, because ofits excellence in adhesion resistance to a ferrous alloy material. And,because of softness thereof, Cu alloy phase dispersed in a martensiteparent phase is abraded slightly by carbide contained in a floating sealmaterial at sliding to form an oil groove, where lubricating oil isreceived, whereby lubricating property of the sliding surface isimproved. Even if a very little heat crack is occurred in a slidingsurface, Cu alloy particles work so as to prevent growing of the heatcrack. Accordingly, in the present invention, it is preferable that thelower limit of a content of Cu alloy phase dispersed in a martensiteparent phase is set at 1% by volume, at which improvement in lubricatingproperty begins to appear. Although a precipitation and a dispersion ofthe Cu alloy phase does not cause brittleness of a floating seal part,increasing an amount of the Cu alloy phase causes decreasing abrasionresistance of the floating seal part due to its softness, whereby it ispreferable that the upper limit of a content of Cu alloy phase dispersedin a martensite parent phase is set at 10% by volume.

A method for forming a martensite parent phase or a martensite parentphase in which cementite is pearlitely dispersed requires a quenchingtreatment, whereby economical efficiency in manufacturing costs becomesa problem. Accordingly, it is preferable that a cooling rate at castingis raised so as to form a martensite parent phase during the castingprocess. A case in which a soft ferrite phase is precipitated in asolidification process has a problem that seizing resistance andabrasion resistance are not improved. Especially, Si is a ferritestabilized element. In a case of a cast iron which has a martensiteparent phase (an austenite parent phases at heating) which form a solidsolution with carbon of 0.15 to 0.5 wt % and contains concentrated Si of2 to 6.5 wt %, ferrite should be easily precipitated. Preventingprecipitation of ferrite requires an addition of austenite stabilizedelement. Accordingly, in the present invention, it is preferable that atleast one or more Mn, Ni and Cu in a total amount of 2 to 7 wt % arecontained in an austenite parent phase.

FIG. 1 is a drawing showing a thermodynamically calculated phase diagramof a mixture of ferrite and austenite and an austenite phase in amaterial containing iron, Si of 4.5 wt %, carbon and M (alloy element).To obtain an austenite parent phase (a martensite parent phase afterquenching) which forms a solid solution with carbon of 0.2 to 0.5 wt %,an addition of austenite stabilized element such as Mn, Ni and Cu workseffectively, and this time, it is preferable that an addition amount ofeach of Mn, Ni and Cu is determined such that as an amount of 0.5×Curepresents half of a real amount of Cu, a total addition amount of Mn,Ni and 0.5×Cu is 2 wt % or more. On the other hand, it is not desirablethat a large amount of alloy elements such as Mo, W and V is containedin austenite. When Mo and W of 1 wt % or more forms a solid solutionwith austenite as described above, Mo special carbide is precipitatedwhereby an action in which Mo and W cause austenite unstable isrestricted. And, since V is precipitated as V₄C₃ (MC-type carbide) andhardly forms a solid solution with austenite, a ferrite stabilizingeffect is restricted. Accordingly, in the present invention, it ispreferable that each amount of Mn, Ni and Cu is determined such that anamount of Mn in a martensite parent phase is set at 2 to 4 wt %, or suchthat as an amount of 0.5×Cu represents half of a real amount of Cu, atotal addition amount of Mn, Ni and 0.5×Cu is within 2 to 7 wt %. And,it is more preferable that Mo and W in a total amount of 1 wt % or lessand Ni of 3 wt % or less are contained.

As a larger amount or cementite or MC-type carbide, described later, isdispersed in a martensite parent phase, abrasion resistance to earth andsand for a floating seal part will be improved; however, conformabilitybecomes deteriorating, whereby a seal contact width becomes narrowremarkably, resulting in occurrence of seizing and heat crack caused byheat generation at a seal sliding surface. Accordingly, it is preferablethat a cast iron constraint at least Mn of 0.7 to 5 wt % so that anamount of Mn in a martensite phase will be adjusted to 2 to 4 wt %, or acast iron contains at least two of Mn of 0.1 to 5 wt %, Ni of 1 to 2.5wt % and Cu of 1 to 10 wt % so that as an amount of 0.5×Cu representshalf of a real amount of Cu, a total addition amount of Mn, Ni and0.5×Cu in a martensite parent phase will be adjusted within the range of2 to 7 wt %. In addition, it is preferable that Ms temperature isadjusted to 95 to 260° C. according to the Ms temperature calculationequation, and retained austenite is contained in a martensite parentphase in 10 to 50% by volume in order to improve conformability andtoughness of a sliding surface.

When a graphitizing treatment is utilized to eutectic cementite in acast iron according to the present invention, it is important to definea relation between a concentration and a degree of graphitization of agraphitizing inhibiting element containing Mn and Mo, other than Cr, anda graphitizing promoting element in the cementite. A concentration CΘMof an alloy element M contained in the cementite is obtained by afollowing equation using a concentration CM of the alloy elementcontained in the cast iron, a dispersion amount VΘ (volume fraction) ofthe cementite and γKM,CΘM=CM×γKM/(1−VΘ+γKM×VΘ)

In the present invention, by applying Cr, Mn, Mo and Ni to the alloyelement M, the follow equation is obtained.2 wt %≦CΘCr+0.3×CΘMn+0.3×CΘMo−CΘNi≦6 wt %

The lower limit of 2 wt % is determined based on the fact that anaddition of Cr of 0.8 wt % will transform a conventional cast iron to awhite cast iron which has eutectic cementite containing Cr of about 1.6wt %. In addition, a coefficient of Mn of 0.3 is determined based on aconcentration of Mn contained in cementite in a white cast iron to whichthe cast iron is transformed by adding Mn of 5 wt %. And, since Mo hassubstantially the same distribution coefficient as Mn, a coefficient ofMo is set at 0.3, as well as Mn. On the other hand, Ni is agraphitization forming element. When a Ni-Hard cast iron is graphitizedat 950° C. for one hour as described later, cementite containing Cr of5.7 wt % and Ni of 1.91 wt % is graphitized in such a short period. Fromthe result, the upper limit is set at 6 wt % and a coefficient of Ni isset at 1, and the upper limit is more preferably 4 wt %.

Specifically, in a conventional cast iron in which cementite isdispersed in 35% by volume, an addition amount of each alloy element isadjusted so as to satisfy the following equation.2 wt %≦0.4×CΘMn+0.4×CΘMo+2.0×CΘCr−0.4×CΘNi≦5 wt %

A half or more amount of retained austenite is transformed to martensiteat sliding, resulting in hardened so as to provide conformability. Onthe other hand, since other unhardened retained austenite is soft, it isexpected to work as the aforesaid oil pocket on a sliding surface.However, a large amount of the soft retained austenite causes decreasingabrasion resistance, whereby it is preferable that an amount of retainedaustenite should be adjusted to 10 to 40% by volume.

Since heightening tempering-softening resistance of a martensite parentphase demonstrates more efficient abrasion resistant sliding property,it is preferable that Si, Al, Mo, V and W improving tempering-softeningresistance significantly are positively added. Especially, Al in amartensite parent phase works to heighten tempering-softening resistanceas well as Si, and an addition of Al of 3 wt % or more begins to causean order-disorder transformation of a Fe₃Al order phase, thereby toimprove remarkable seizing resistance. Furthermore, when Al coexistswith Ni and Co, remarkable age-hardening appears and as a result, Al isdischarged from cementite and concentrated in a martensite parent phaseas well as Si. Accordingly, in the present invention, it is preferablethat a cast iron contains at least Al of 0.5 to 6 wt % so that an amountof Al in a martensite parent phase will be adjusted to 1 to 12 wt %.And, it is preferable that at least either Ni of 1 to 7 wt % or Co of 2to 15 wt %, and Al of 1 to 6 wt % are added to the cast iron.

Co increases magnetic transformation remarkably thereby to decrease adistribution coefficient of carbon and an alloy element, resulting inincreasing tempering-softening resistance of Mo, V, W, Al, Si and thelike. Accordingly, in the present invention, it is preferable that Co of15 wt % or less is added from an economical viewpoint.

In the present invention, in order to disperse Cu alloy phase in themartensite parent phase in 1 to 10% by volume, it is preferable that Cuof at least 1 to 10 wt % is added to a material used for a castingfloating seal. And, in order to increase seizing resistance of Cu alloyphase, it is preferable that a cast iron abrasion resistant slidingmaterial has Cu alloy phase dispersed therein, wherein the Cu alloyphase comprises Cu—Si—Al alloy containing a mixture of Si and Al of 3 to12 wt %. Alternatively, a β phase or an intermetallic compound phase ispreferably dispersed therein. MC-type carbide is mainly formed by V, W,Ti, Zr, Nb and Ta and is the hardest carbide thereby to contribute toimprovement in abrasion resistance. However, the MC-type carbide haslittle solid solubility with cementite, whereby it hardly stabilizescementite and does not prevent precipitation of graphite. Accordingly,in a cast iron abrasion resistant sliding material according to thepresent invention, one or more alloy element selected from the groupconsisting of V, Ti, Zr, Nb and Ta is added in a total content of 1 to5% by volume so that one or more MC-type carbide, nitride andcarbonitride will be dispersed in a total content of 2 to 10% by volume,whereby abrasion resistance can be improved. For example, in the case ofTiC as MC-type carbide, by using a specific gravity of TiC of 4.9 g/cm³,an addition of Ti of 1 to 5 wt % disperses TiC of 2 to 10% by volume,and thus, abrasion resistance is effectively improved. The reason thatthe upper limit of an addition amount of the alloy elements is 5 wt % isthat an amount of MC-type carbide in the aforesaid high speed steel doesnot exceed about 10% by volume. And, if it exceeds 5% by volume, initialconformability for a floating seal part becomes less efficient.

And, since dispersing phosphide and MC-type carbide in a small amountimproves seizing resistance of a sliding surface remarkably, suchparticles dispersion effect is also expected by dispersing compoundsother than the phosphide. Accordingly, in the present invention, it ispreferable that phosphide of mainly one or more alloy element of Fe, Vand Ti is dispersed in a total content of 0.2 to 5% by volume (morepreferably, 1 to 5% by volume), or sulphide of at least either Mn or Tiis dispersed in a total content of 0.2 to 5% by volume (more preferably,1 to 5% by volume), or the both of the phosphide and the sulphide aredispersed in a total content of 0.2 to 5% by volume (more preferably, 1to 5% by volume).

In the present invention, it is possible that a floating seal part isformed by casting using the aforesaid ferrous seal sliding material andthe aforesaid cast iron abrasion resistant sliding material. And, it ispreferable that a ferrous seal sliding part, for example, a floatingseal, is formed by casting using the aforesaid cast iron.

And, it is more preferable that the ferrous seal sliding part and thefloating seal part are formed by a centrifugal casting method using aquenching chilled cast iron. At this time, it is still more preferablethat a mold is heated to the Ms temperature or more of a parent phase ofthe cast iron and then the centrifugal casting method is applied theretoso as to produce a floating seal part. And, after releasing the floatingseal part from the mold at the Ms transformation temperature or more,the floating seal part is quench hardened so as to prevent occurrence ofcrack and strain at casting.

A producing method of a ferrous seal sliding part according to thepresent invention comprises a step for casting a cast iron containingcarbon of 2 to 5 wt %, Si of 0.5 to 6 wt %, Cr of 0.3 to 5 wt % and oneor more alloy element selected from the group consisting of Al, Mn, Ni,Cu, Co, Mo, W, V, Ti, Zr, Nb, Ta, O, B, Ca and S.

It is preferable that the ferrous seal sliding part has a martensiteparent phase which forms a solid solution with carbon of 0.15 to 0.6 wt% and contains a first dispersion material of at least either cementiteof 5 to 70% by volume or MC-type carbide of 0.1 to 10% by volume and asecond dispersion material of at least either graphite of 1 to 15% byvolume or Cu alloy phase of 1 to 20% by volume dispersed therein, with atotal content of the first dispersion material and the second dispersionmaterial being 5 to 70% by volume.

In the present invention, it is possible that the casting step is forcasting the cast iron by a centrifugal method, using a mold which isheated to Ms temperature or more of a parent phase of the cast iron, andquenching the cast iron after releasing from the mold. At this time, itis also preferable that, after the casting step, a step for re-heatingthe cast iron at Al transformation temperature or more of the cast ironand then graphitizing is carried out before the quenching step.

Next, a cast iron abrasion resistant sliding material according to thepresent invention will be described in detail with reference to theaccompanying drawings.

FIG. 2 is a drawing showing a main part of a roller assembly accordingto one embodiment of the present invention. This embodiment shows afloating seal member equipped with the roller assembly.

The roller assembly 36, according to the embodiment, has a rollerretainer 49, a roller shaft 50 supported by the retainer 49 and a rollerbush 51 fitted onto the shaft 49, which are rotatably connected eachother. A floating seal member 53 is provided with one pair of seal rings54 with seal surfaces contacted each other and an O-ring 55 fitted ontoeach of the seal ring 54. In the roller assembly 36, the floating sealmember 53 is arranged such that the contacted seal surfaces of the sealrings 54 are pressed toward the roller shaft 50 by elastic force of thecompressed O-rings 55. The seal surfaces are relatively slidable whilebeing pressed each other at an adequate pressure so as to prevententering water or earth and sand from outside, as well as preventingleakage of lubricating oil from inside.

The seal surface of the seal rings 54 has a structure which contains atleast either cementite of 5 to 70% by volume or MC-type carbide of 1 to10% by volume and at least either graphite or Cu alloy phase dispersedin a hard martensite parent phase.

In a large diameter floating seal part used for a reduction gearapparatus, a diameter of the seal ring becomes so large that a slidingrate of the seal surface becomes high. Accordingly, a floating seal ringexcellent in higher seizing resistance and higher heat crack resistanceis required. In order to obtain such floating seal ring, in the presentinvention, it is preferable that at least either graphite or Cu alloyphase in a total content of 3 to 10% by volume is dispersed in amaterial for a cast floating seal used at a sliding rate of 1 m/sec ormore.

The present invention can provide a floating seal part excellent inseizing resistance and heat crack resistance. In order to furtherimprove heat crack resistance and seizing resistance, it is preferablethat an addition amount of an alloy elements such as Si, Cr, Cu, Mo, Wand V is regulated so that a solid soluble concentration of carbon witha martensite parent phase will be adjusted to 0.15 to 0.7 wt %, and thatrapidly heating quenching, in which a quenching temperature is set at850 to 1000° C. and a quenching rate is 150° C./sec or more, is carriedout. And, it is also preferable that cementite is prepared so as to havea magnetic transformation temperature within the range of 60 to 180° C.by using V, Mn and Cr mainly, and so as to disperse at least eithergraphite or Cu alloy phase promoting lubricating property, therein. Inaddition, it is also preferable that an addition amount of each of Siand Cr is adjusted so that a solid soluble concentration of carbon witha martensite parent phase will be 0.15 to 0.6 wt %, that a total amountof Si and Al is heightened up to 4 wt % or more to provide anorder-disorder transformation, that MC-type carbide, phosphide andsulphide showing a hard particles dispersion effect are dispersed in amartensite parent phase, and that at least either graphite or Cu alloyphase promoting lubricating property are dispersed in a martensiteparent phase. And, it is also preferable that Curie temperature ofcementite contained in a cast iron is adjusted to 60 to 150° C. by usingV, Mn and Cr so that endothermic phenomenon will appear when alubricating oil on a sliding surface begins to deteriorate. When aquenching treatment is carried out after graphitizing to dispersegraphite, it is preferable to be rapidly heated at a temperature risingrate of 150° C./sec or more to a quenching temperature within the rangeof 850 to 1050° C. by induction heating capable of rapidly heating, andthen cooling, thereby to disperse pearlitely platy cementite andgranulated cementite, in addition to eutectic cementite and granulatedgraphite, in the martensite parent phase.

FIG. 3 are drawings showing various structures of graphite crystallizedand dispersed in a cast iron formed by casting. FIG. 3A shows graphiteflake, FIG. 3B shows spheroidal graphite, and FIG. 3C shows vermiculargraphite. Each of the graphite which appears in a large amount at asolidification process has a parent phase each having a ferrite,acicular ferrite, pearlite, bainaite and martensite structures. Thepresent invention provide a cast iron abrasion resistant slidingmaterial, which is formed such that a cast iron which should have apearlite structure by addition of Cr of 0.3 wt % or more is rapidlycooled at a solidification process to transform a parent phase to amartensite structure which contains MC-type carbide dispersed therein in1 to 10% by volume.

FIG. 4A is a photograph showing a casting structure of a Ni-hardcomparative material, in example described later, and FIG. 4B is aphotograph showing a heat treated structure thereof after graphitizing.As shown in FIG. 4A, a chilled cast iron has a structure in which alarge amount of eutectic cementite is dispersed in a martensite parentphase. And, in a case in which the chilled cast iron is subjected tographitizing at 950° C. and then directly quenched from suchtemperature, the original structure is changed to a structure, as shownin FIG. 4B, in which coarse cementite is decomposed to precipitate finegranulated graphite, and as a result, the granulated graphite anduniformly dispersed undecomposed eutectic cementite are dispersed in amartensite parent phase. Such structure is preferable for the purpose ofimprovement in toughness.

Solid solubility of Cu with a parent phase of a cast iron abrasionresistant sliding material, which varies according to amounts of carbon,Ni and Mn, is about 5 to 6 wt %. Accordingly, by adding Cu of 7 wt % ormore, a cast iron having a structure in which Cu alloy phase isgranulately dispersed can be obtained. The structures in which Cu alloyphase is dispersed in each of structures, as shown in FIG. 3 and FIG. 4,are therefore included in the category of the present invention.

In order to improve seizing resistance of abrasion resistance of a castiron abrasion resistant sliding material, it is preferable that carbidesuch as cementite or V₄C₃ is dispersed.

EXAMPLE

A cast iron abrasion resistant sliding material will be explained withreference to the accompanying drawings.

In this example, casting floating seal materials and casting comparativematerials shown in Table 1 were used. Each of the material was cast in ashell-shaped mold to prepare comparative fusil specimens. On the otherhand, after being cast in a shell-shaped mold, each of materials wasre-heated (graphitized) at 950° C. and then quenched to prepare fusilspecimens. Then, each of the comparative fusil specimens and the fusilspecimens were machined to have a floating seal shape, as shown in FIG.5, and then lapping treatment was applied to a seal surface (shown inthe figure) thereof. Then, seizing resistance of each of the sealsurface of both specimens was measured by using a floating seal tester,as shown in FIG. 6. TABLE 1 COMPOSITION (wt %) AND PV VALUE OF MATERIALSAs Cast 950° C. PV PV No. C Si Mn Ni Cr Mo V Co W P Al Cu VALUE 1 VALUE2 No. 1 3.79 1.05 0.88 2.05 0.97 0.01 0.03 1.8 2.4 No. 2 3.81 2.01 0.862.01 0.93 0.01 0.03 2.8 3.6 No. 3 2.21 1.02 1.11 2.36 0.74 0.51 2.5 3.1No. 4 3.71 2.12 1.55 1.02 0.32 2.51 0.02 3.3 3.9 No. 5 3.63 2.99 1.084.01 1.03 0 3.9 4.6 No. 6 3.78 3.01 0.85 3.91 1.01 0.49 4.1 4.9 No. 72.95 3.65 2.02 2.03 0.91 0.02 0.03 4.2 5.0 No. 8 3.77 2.63 2.01 2.200.59 0.14 4.11 0.04 3.6 5.4 No. 9 3.64 1.53 1.89 2.01 0.72 1.22 2.7 3.2No. 10 3.68 1.51 1.91 2.1 0.31 1.56 0.02 2.5 3.3 No. 11 3.52 2.01 0.812.02 0.51 0 0.01 4.91 2.5 3.6 No. 12 3.35 2.66 0.77 2.29 1.03 0.16 0.029.70 3.4 4.2 No. 13 3.31 1.51 0.85 3.98 1.05 0.16 0.03 2.05 9.50 3.8 4.7No. 14 3.65 1.01 1.55 4.52 1.04 0.16 0.02 3.51 3.7 5.3 CHILLED CAST IRON3.53 0.88 0.62 0.05 0.01 0.01 0.11 1.65 1.4 2.1 Nihard 3.12 0.96 0.474.22 3.17 0.01 0.02 2.1 3.2 FC₁₅Cr₃Mo 3.56 1.58 0.59 2.21 15.5 2.31 0.441.8 FC₉Cr₆Mo 3.20 1.22 0.51 1.70 9.20 6.10 2.13 4.98 4.92 2.5

The floating seal tester used a floating seal member, in which each ofthe prepared fusil floating seal specimens was used as a pair of sealrings with the seal surfaces contacted each other. And, an O-ring whichpressed one of the seal ring was rotated around a central axis of theseal rings with respect to a fixed O-ring which pressed another sealring with applying load. The seizing resistance was evaluated by using aPV value. The PV value was obtained by product of P (pressure) and V(revolution rate) when seizing resistance rapidly increased whilechanging a rotating rate (a revolution rate V) under a condition inwhich press load between the seal surfaces was kept at 63 kgf (presspressure P was 2 kg/cm, the press pressure was a load per a seal surfacelength) to enclose engine oil (EO#30). The results are shown in columnsof “PV value 1” and “PV value 2” in the table 1. The “PV value 1” showsa PV value of the comparative fusil specimens, in which the castingfloating seal materials and the casting comparative floating sealmaterials were cast only. On the other hand, the “PV value 2” shows a PVvalue of the fusil specimens, in which the casting floating sealmaterials and the casting comparative floating seal materials werere-heated (graphitized) at 950° C. after casting, and then quenched. Inaddition, a solid soluble concentration of carbon in a martensite parentphase, a dispersive power of cementite, a concentration of alloy elementin a parent phase and a concentration of alloy element in cementite ofchilled cast iron, which are calculated by using a distributioncoefficient of each metal element, are shown in Table 2. TABLE 2COMPOSITION (CONCENTRATION OF ALLOY ELEMENT et.al OF MATERIALS) γKM.DISTRIBUTION COEFFICIENT OF ALLOY ELEMENT As Cast 950° C. COMPOSITION(wt %) OF ALLOY SOLID ELEMENT IN MARTENSITE COMPOSITION (wt %) SOLUBLEγKM= OF ALLOY ELEMENT DEGREE CARBON VOLUME 0 1.9 0.3 4. 2.3 6. 0 0 0 INCEMENTITE OF No. (%) OF θ (%) Si Mn Ni Cr Mo V P Al Cu Mn Ni Cr MoGRAPHITIZATION No. 1 0.56 0.48 2.0 0.62 3.08 0.40 0.01 0.00 0.06 0.0 0.01.17 0.92 1.59 0.01 1.85 No. 2 0.36 0.52 4.0 0.59 3.08 0.37 0.01 0.000.06 0.0 0.0 1.13 0.92 1.50 0.01 1.72 No. 3 0.62 0.22 1.3 0.92 2.80 0.440.00 — 0.00 0.0 0.0 1.76 0.84 1.78 0.00 2.69 No. 4 0.43 0.42 3.5 1.141.41 0.15 0.00 — 0.03 0.0 0.0 2.17 0.42 0.58 0.00 2.33 No. 5 0.18 0.525.8 0.75 6.07 0.42 0.00 — 0.00 0.0 0.0 1.43 1.82 1.68 0.00 1.29 No. 60.17 0.53 5.9 0.59 5.97 0.41 0.00 — 0.00 0.0 0.0 1.12 1.79 1.63 0.000.96 No. 7 0.16 0.42 6.0 1.49 2.79 0.42 0.01 — 0.05 0.0 0.0 2.84 0.841.68 0.03 3.71 No. 8 0.35 0.39 4.2 1.51 2.97 0.28 0.09 — 0.06 0.0 0.02.86 0.89 1.12 0.22 3.31 No. 9 0.49 0.47 2.8 1.34 2.96 0.30 0.00 — 0.300.0 0.0 2.54 0.89 1.21 0.00 2.86 No. 10 0.51 0.48 2.8 1.35 3.09 0.130.98 — 0.04 0.0 0.0 2.57 0.93 0.52 2.25 4.41 No. 11 0.42 0.47 3.6 0.582.94 0.22 0.00 — 0.02 0.0 8.9 1.10 0.88 0.87 0.00 1.09 No. 12 0.28 0.464.7 0.55 3.30 0.45 0.10 — 0.04 0.0 17.2 1.05 0.99 1.78 0.23 2.08 No. 130.50 0.42 2.6 0.62 5.61 0.47 0.10 — 0.05 3.5 16.2 1.18 1.68 1.87 0.241.60 No. 14 0.57 0.46 1.9 1.10 6.65 0.44 0.10 — 0.04 6.5 0.0 2.09 2.001.75 0.23 2.07 CHILLED 0.65 0.43 1.5 0.45 0.07 0.00 0.01 — 0.19 0.0 2.90.85 0.02 0.02 0.01 0.86 CASTIRON Nihard 0.50 0.39 1.6 0.34 5.92 1.420.01 — 0.03 0.0 0.0 0.65 1.78 5.69 0.02 4.58 FC₁₅Cr₃Mo — FC₉Cr₆Mo —

In the Table 2, No. 1 and No. 2 are alloy elements related Ni-hardchilled cast iron of the casting comparative materials. As compared achilled cast iron and a Ni-hard cast iron of the comparative materialswith No. 1 and No. 2, it is found that increasing an amount of Sidecreases a solid soluble concentration of carbon with a martensiteparent phase, whereby seizing resistance is improved. And, it is alsofount that graphite which is dispersed and precipitated by the heattreatment (a heating temperature of 950° C. and a heating period of onehour) improves seizing resistance of the seal surface. FIG. 4A and FIG.4B are photographs showing typical structures of a Ni-hard cast iron.From the figure, it is found that fine graphite particles having anaverage grain size of about 5 μm, which does not cause leakage of oil onthe seal surface and evenly dispersed eutectic cementite particles aredispersed. However, remarkably decreasing eutectic cementite occurs,resulting in lack of abrasion resistance. Accordingly, such Ni-hard castirons are suitable for a seal member required smaller abrasionresistance to earth and sand.

No. 3 and No. 4 are standards containing NC-type carbide (V₄C₃) of Vdispersed therein with respect to No. 1 and No. 2 on the point ofimprovement in abrasion resistance. It is found that dispersing V₄C₃carbide improves seizing resistance and abrasion resistance. And, it isobserved that graphite is precipitated by graphitization, as a result,seizing resistance is improved by dispersion of graphite particles.Accordingly, they are suitable for a floating seal material requiredseizing resistance. Thus, it is also preferable to add an alloy elementsuch as Ti, Zr, Nb and the like, which causes precipitation anddispersion of MC-type carbide, substitute for V. Especially, Ti is morepreferable since it does not prevent graphitization.

No. 5, No. 6, No. 7 and No. 8 are materials in which an addition amountof Si is increased so as to have a concentration of Si in a martensiteparent phase of 5 wt % or more in order to demonstrate an order-disordertransformation of Fe₃Si, and further to disperse V₄C₃ carbide therein.It is found that floating seal materials excellent in seizing resistanceand abrasion resistance are obtained. In No. 8, to which V is added in ahigh density to disperse a large amount of V₄C₃, since a large amount ofretained austenite remains by increasing an addition amount of Mn,whereby conformability of the seal surface is improved, thereforeseizing resistance is more improved.

No. 9 and No. 10 are materials to which an increased amount of Mn isadded so as to increase an amount of retained austenite in a martensiteparent phase with the eutectic cementite, eutectic cementite andgraphite particles dispersed therein, whereby tempering-softeningresistance is heightened, in addition to an effect in which Fe₃Pphosphide are dispersed and an addition of Mo to the martensite parentphase. From the result, seizing resistance higher than that of thecasting comparative material is obtained. And, dispersing sulphidesubstitute for phosphide also improves seizing resistance.

No. 11 and No. 12 are standards in order to confirm an effect ofdispersion of Cu alloy phase. Increasing a dispersion amount of Cu alloyphase improves seizing resistance. Especially, No. 13, in which Cu alloyphase containing Al are dispersed, improves seizing resistance more thanNo. 11 and No. 12. Accordingly, seizing resistance may be improved byincreasing an amount of Cu—Si—Al alloy phase.

No. 14 is a standard in which a Fe₃Ai order-disorder transformation isheightened by adding of Al. Seizing resistance is improved, and agehardening is obtained by increasing of an addition amount of Ni, wherebyexcellent seizing resistance is demonstrated. And, it is effective forimproving abrasion resistance to disperse MC-type carbide in thesestandards.

The present invention is not limited to any of the above-describedconstructions and embodiments, and various modifications of the presentinvention can be made without departing from the technical ideas.

1-15. (canceled)
 16. A producing method of a ferrous seal sliding parthaving a step for casting a cast iron containing carbon of 2 to 5 wt %,Si of 0.5 to 6 wt %, Cr of 0.3 to 5 wt % and one or more alloy elementselected from the group consisting of Al, Mn, Ni, Cu, Co, Mo, W, V, Ti,Zr, Nb, Ta, P, B, Ca and S, wherein said seal sliding part has amartensite parent phase which forms a solid solution with carbon of 0.15to 0.6 wt % and contains a first dispersion material of at least eithercementite of 5 to 70% by volume or MC-type carbide of 0.1 to 10% byvolume and a second dispersion material of at least either graphite of 1to 15% by volume or Cu alloy phase of 1 to 20% by volume dispersedtherein, with a total content of said first dispersion material and saidsecond dispersion material being 5 to 70% by volume.
 17. A producingmethod of a ferrous seal sliding part according to claim 16, whereinsaid casting step is for casting said cast iron by a centrifugal method,using a mold which is heated to Ms temperature or more of a parent phaseof said cast iron, and quenching said cast iron after releasing fromsaid mold.
 18. A producing method of a ferrous seal sliding partaccording to claim 16, wherein, after said casting step, a step forre-heating said cast iron at Al transformation temperature or more ofsaid cast iron and then graphitizing is carried out before saidquenching step.